P = U * I * cosφ, cosφ it represents the power factor, purely resistive load (Such as incandescent, heater, etc.) the power factor is generally close to 1,Between the inductive and capacitive load load power factor 0-1. So purely resistive load test time, P is substantially equal to or close to U * I. When Inductive or capacitive load test (Such as refrigerators, washing machines, televisions, computers, etc.) P<U*I, As for how much to keep the power factor related to the specific, Different for each appliance power factor.